1. Field of the Invention
The present invention relates to a photodetection method and photodetection device and photodetection/light emission device that are utilized for example in a photodetection unit for optical communication using infra-red rays.
2. Description of the Related Art
Photodetection devices of this type are provided at the fiber tip part in information communication devices using for example optical fibers and are constituted by a combination of a single lens and a photodetection element. A conventional known photodetection devices are illustrated in FIGS. 11(a), (b), (c), (d) and (e). In these Figures, 1 is a photodetection element, and 2 is a condenser lens arranged in front of it; condenser lens 2 is usually integrated with a photodetection element package (constituted by transparent resin in which a photodetection element 1 is molded).
As shown in FIGS. 11(a), (b) and (c), the shape of the condenser lens may be flat, semi-cylindrical, or cylindrical but, if no modification is made to this, suffers from the defect that it easily admits external optical interference such as light from fluorescent lamps or incandescent lamps arriving at the optical input face and constitutes a source of photodetector noise, because of its wide half-value angle of about xc2x160xc2x0.
In order to deal with this drawback the following proposals have been made:
(1) to restrict the half-value angle to to xc2x130xc2x0 or xc2x115xc2x0 by suitably modifying the lens shape of the semi-cylindrical or hemispherical lens;
(2) as shown in FIG. 11(d), to provide an external interference exclusion section 3 connected to both sides or one side of semi-cylindrical condenser lens 2 (see Japanese Utility Model Number 2561800): or
(3) as shown in FIG. 11(e), to cover the parts other than the central part of condenser lens 2 with a screening element 4 (Laid-open Japanese patent publication H. 8-330608, Japanese patent number 2651756).
However, the above proposals (1) to (3) had the following drawbacks.
In the case of (1), since the photodetection e.m.f. is not fixed within the half-value angle, although there is a large photodetection e.m.f. in respect of light from directly in front, as the photodetection angle is increased, the photodetection e.m.f. gradually falls. Consequently, as shown in FIGS. 12(A) and (B), the photodetection angular efficiency is poor when it is below 50%. FIG. 12(A) shows characteristic in the case of suitably modifying the shape of the cylindrical lens shown in FIG. 11(c), and FIG. 12(B) shows characteristic in the case of suitably modifying the shape of the semi-cylindrical lens shown in FIG. 11(b).
In the case of (2), the presence of the interference exclusion section 3 renders the shape complicated and restricts the possibilities for miniaturization.
In the case of (3). Only a very small portion of the incoming light reaches photodetection element 1, so the photodetection e.m.f. is very weak. Also, since the screening effect in regard to interfering light that gets in from the apertures of screening element 4 is poor there is a limit to the extent to which the effect of optical interference can be excluded. Also, since a screening element must be provided separately from condenser lens 2, manufacturing costs are high.
Further, in the cases of (2) and (3), the designs are such that incoming light from directly in front converges onto the photodetection surface of photodetection element 1 so when the optical intensity arriving at this point is high there is a risk of the output of this point of convergence becoming saturated. Also, since the output of the areas to which convergence does not take placed is normally practically zero, if the angle of photodetection changes, causing the point of convergence to shift, the reaction time is prolonged, with the risk that response to signal changes may be delayed. Furthermore, since the photodetection e.m.f. is unstable at angles where the light is converging onto a contaminated or defective portion of photodetection element 1, the output tends to be easily affected by photodetection angle. Also, since photodetection element 1 is arranged at the position of the focal point, a large distance is required between the surface of condenser lens 2 and photodetection element 1, which limits possibilities for miniaturizing the device.
In view of the foregoing, an object of the present invention is to provide a photodetection method and photodetection device and photodetection/light emission device wherein there is no possibility of optical interference being picked up, which has a stable photodetection e.m.f. in a prescribed region, and which has high photodetection angular efficiency.
The following are means for resolving the above-mentioned issues.
A first aspect of the present invention is a method of photodetection, wherein photodetection is performed with a condenser lens positioned in front of a photodetection element, in which: as said condenser lens, a non-spherical lens is employed that concentrates at a single point without spherical aberration light that is input from the optic axis direction of this lens; and by positioning said photodetection element such that the photodetection surface of said photodetection element is further towards the lens than the point of convergence of said condenser lens, it is arranged that light that has passed through said condenser lens is photodetected over most of the photodetection surface of said photodetection element and that said photodetection element is positioned in a position where it can photodetect all of light that is incident inclined at a prescribed angle with respect to the optic axis of said condenser lens.
A second aspect of the present invention is a photodetection device, wherein photodetection is performed with a condenser lens positioned in front of a photodetection element, in which: as said condenser lens, a non-spherical lens is employed that concentrates at a single point without spherical aberration light that is input from the optic axis direction of this lens; and by positioning said photodetection element such that the photodetection surface of said photodetection element is further towards the lens than the point of convergence of said condenser lens, it is arranged that light that has passed through said condenser lens is photodetected over most of the photodetection surface of said photodetection element and that said photodetection element is positioned in a position where it can photodetect all of light that is incident inclined at a prescribed angle with respect to the optic axis of said condenser lens.
A third aspect of the present invention is a is photodetection device, according to aspect 2, wherein said photodetection element is positioned in the position closest to said condenser lens in the range in which it can photodetect all of light incident at a prescribed angle with respect to said condenser lens.
A fourth aspect of the present invention is a photodetection device, according to aspect 2, wherein the shape of the curved surface of the non-spherical surface of said non-spherical lens is a shape expressed by the following expression:
xe2x80x83f(x)=(1/R)xc2x7[x2/[1+{1+A xc2x7(x/R)2}1/2]]+Bx4+Cx6+Dx8+Ex10
where R is the radius of curvature, x is the distance from the center of the lens, A, B, C, D and E are coefficients of the non-spherical surface, and f(x) is the lens shape when the distance is x.
A fifth aspect of the present invention is a photodetection device, according to aspect 4, wherein R=1.67793 and A=xe2x88x920.66229.
A sixth aspect of the present invention is a Photodetection device, according to aspect 4, wherein R 1.72732 and A=xe2x88x920.28636.
A seventh aspect of the present invention is a Photodetection device, according to aspect 2, wherein the 95% photodetection e.m.f. range is within xc2x130xc2x0, the 50% photodetection e.m.f. range is within xc2x147xc2x0, and the photodetection angular efficiency is 66% or better; where: the 95% photodetection e.m.f. range means the range of photodetection angle (angle made by the incident light with respect to the optic axis of the lens) for which the photodetection e.m.f. (magnitude of the voltage generated in the photodetection element by light that is incident onto the photodetection element) is 95% of the maximum value; the 50% photodetection e.m.f. range means the range of photodetection angle for which the photodetection e.m.f. is 50% of the maximum value; and the photodetection angular efficiency means the ratio of xe2x80x9crange of 95% photodetection e.m.f.xe2x80x9d/xe2x80x9crange of 50% photodetection e.m.f.xe2x80x9d expressed as a percentage value.
A eighth aspect of the present invention is a Photodetection device, according to aspect 2, wherein said photodetection element is packaged integrally with said condenser lens using the said material that constitutes said condenser lens.
A ninth aspect of the present invention is a photodetection device, according to aspect 8, wherein epoxy resin is employed as the material constituting said condenser lens.
A tenth aspect of the present invention is a photodetection device, according to aspect 8, wherein the surface roughness of the optical functioning surface of said condenser lens is below 1 micrometer in terns of arithmetical average roughness.
A eleventh aspect of the present invention is a photodetection device, according to aspect 8, wherein said photodetection element is mounted on a lead frame.
A twelfth aspect of the present invention is a photodetection device, according to aspect 11, wherein said lead frame is constituted of copper.
A thirteenth aspect of the present invention is a photodetection device, according to aspect 11, wherein said lead frame is of a construction capable of being mounted on a circuit board.
A fourteenth aspect of the present invention is a photodetection/light emission device in which a light-emitting unit and photodetection unit are integrally mounted, a photodetection device according to aspect 2 being employed for said photodetection unit.
FIGS. 1(a) and (b) are cross-sectional views of an embodiment of the present invention, FIG. 1(a) being the case where the incoming light has an angle and FIG. 1(b) being the case where the incoming light does not have an angle;
FIGS. 2(a),(b) and (c) are views given in explanation of part of the procedure when designing a photodetection device according to an embodiment of the present invention, FIG. 2(a) being the case where the light passing through the lens does not converge at a single point, FIG. 2(b) being the case where the light passing through the lens does converge at a single point, and FIG. 2(c) being the case where the incoming light is inclined;
FIGS. 3(A) and (B) are views showing a photodetection e.m.f. curve according to an embodiment of the present invention;
FIG. 4 is a view given in explanation of a method of measurement for obtaining a photodetection e.m.f. curve;
FIG. 5 is a view illustrating a comparison of an embodiment of the present invention with a prior art example;
FIG. 6 is a view illustrating a first specific example of the appearance of a photodetection device;
FIG. 7 is a view illustrating a second specific example of the appearance of a photodetection device:
FIG. 8 is a view illustrating a third specific example of the appearance of a photodetection device;
FIG. 9 is a view illustrating a fourth specific example of the appearance of a photodetection device:
FIG. 10 is a view illustrating a fifth specific example of the appearance of a photodatection device:
FIGS. 11(a),(b),(c),(d) and (e) are views illustrating examples of a prior art photodetection device; and
FIGS. 12(A) and (B) are views showing a photodetection e.m.f. curve according to a prior art example.